The invention relates to a method and an apparatus for determining the composition of the mixture fed to an internal combustion engine by sensing the magnitude of operational engine parameters.
Several methods are known for regulating the composition of a fuel-air mixture in an internal combustion engine so as to obtain exhaust gases as free from toxic components as possible. For example, the engine may be regulated to operate with a stoichiometric mixture having an air number .lambda.=1.
For this purpose, operational parameters of the engine are sensed, for example the exhaust gas composition, with the aid of an oxygen sensor which measures the presence of free oxygen in the exhaust gas of the engine. Such known oxygen sensors have the advantage of generating a clear and regular control signal during the transition from a hyperstoichiometric to a hypo-stoichiometric mixture and vice versa when the air number .lambda. traverses the value 1.0 but they have the disadvantage of being fairly expensive since they have a platinum containing surface material and their life time is relatively short because of thermal and mechanical loads.